An example of a small lamp using a wedge base bulb of the prior art is described in Japanese Examined Utility Model Publication No. 53-1825.
This example of the prior art is a small interior lamp for automobile use equipped with a housing, a lens located in the opening of the housing, a holder attached to the housing, and a wedge base bulb supported in the holder. The holder is composed of a holder body, formed by bending a conductive metal strip into the shape of the letter "U", and an attachment piece integrated into a single unit with the holder body and extending in the opposite direction from the U-shaped conductive metal strip. An engaging indentation is formed with the holder body in the housing. A center piece and right and left side pieces are provided in opposition at an interval protruding from the top and bottom of the engaging indentation. The U-shaped portion of the holder body is clamped between the center piece and the left and right side pieces by fitting into the engaging indentation wherein the holder body is formed in the housing. In this state, the attachment piece of the holder body is fixed in the housing together with a conducting strip for connection.
Since the prior art described above comprises an interior lamp by directly forming a wedge base bulb portion in a portion of an interior lamp housing and inserting a connector, looseness occurs due to thermal deformation of the bulb holder caused by the generation of heat accompanying lighting of the above-mentioned bulb. Although the above-mentioned bulb holder portion should be molded with heat-resistant plastic together with a large-volume housing in order to prevent this loosening, this results in the first disadvantage of the prior art wherein the use of heat-resistant plastic is both expensive and difficult to mold, thus resulting in high costs.
In addition, the prior art also had the second disadvantage of the connector peripheral members, such as the above-mentioned bulb holder, having a complex structure, which together with requiring post-processing such as caulking, made automated insertion of the connector as well as automated assembly of the interior lamp by automated wiring extremely difficult.